


public class MyQueque {
    static class ListNode{
        public int val;
        public ListNode prev;
        public ListNode next;
        public ListNode(int val){
            this.val=val;
        }
    }
    public ListNode head;
    public ListNode last;
    public void offer(int val){

        ListNode node = new ListNode(val);
        if(head == null){
            head = last =node;
        }else {
            last.next = node;
            node.prev = last;
            last = last.next;
        }

    }
    public int poll(){
        if(head == null){
            return -1;
        }
        int ret = head.val;
        if(head.next == null){
            head = null;
            last = null;
        }else {
            head= head.next;
            head.prev = null;

        }
        return ret;
    }
    public int peek(){
        if(head == null){
            return -1;
        }
        return head.val;
    }
    public boolean isEmpty(){
        return head == null;
    }

}
